NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Development and Analysis of a Swept Blade 

Aeroelastic Model for a Small Wind Turbine

Robert Preus, Rick Damiani, and Sang Lee

National Renewable Energy Laboratory

Scott Larwood

University of the Pacific

Small Wind Conference

June 17, 2014

Stevens Point, Wisconsin

PR-5000-62197
2

Acknowledgments

• U.S. Department of Energy (DOE) – For 

Competitiveness Improvement Project (CIP) funds 

and computer-aided engineering (CAE) tools funds

• Scott Larwood – For implementing the original 

version of FAST2ADAMS in FAST6

• Reference turbine loosely based on Bergey Wind 

Power Excel S10.
3

Outline

• Quest towards optimized/advanced rotors

• CAE tools: FAST and ADAMS

• Case study

• Summary of results.
4

• Reduce loads at current rotor diameter 

OR

• Increase rotor diameter at same loading level

• Reduce material

• Optimize utilization

• Reduce the levelized cost of energy (LCOE).

Why Advanced Rotors?
5

• The lift at the tip induces 

pitch-feather

Blade SweepBend-Twist Coupling

Courtesy of Wetzel Engineering, Inc.

• Load mitigation:

reduce ultimate and fatigue 

loads

Viryd CS-8 wind turbine under test at the National 

Wind Technology Center, Photo by Mark Murphy, 

NREL 22258
6

• FAST– Aero-Hydro-Servo-Elastic CAE Tool in Development Since 1996:

o Open source = FREE!

o Capable of simulating tail and 

 furling dynamics for small wind

o Twenty-four degrees of freedom (DOFs) 

horizontal-axis wind turbine only—

vertical-axis wind turbine aerodynamics

 captured in upcoming V8

o Use for design to International 

Electrotechnical Commission load cases –

certification

o V8 will be capable of blade torsional 

 (twist) degree of freedom

o Can be used to prepare ADAMS 

 input files and models.

CAE Tools: FAST and ADAMS
7

• MSC ADAMS – Multibody Dynamics:

o Commercial product

o Can be coupled to Aerodyn (FAST module) – FAST2ADAMS available for FREE

o Can be highly customizable with user’s controller library (requires a bit of 

programming)

o Highly flexible – virtually any geometry you can think of

o High fidelity – as many DOFs as the user requires.

CAE Tools: FAST and ADAMS (continued)
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• Original preprocessor would use the sheared approach:

o Leads to inaccurate representation of aerodynamic and inertial loads 

• New preprocessor follows curved properties of blade elements:

o Higher fidelity and physically consistent results

o Improved accuracy.

FAST2ADAMS
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• Started the case study from a much simpler FAST input model 

and created an ADAMS model of a small wind turbine

• Small wind research turbine (SWRT) baseline rendering

• Design load cases (DLCs): 1.1 from 61400-2,NTM, WS 8–16 m/s

• Five configurations: baseline and 0, 5, 10, 15, 20 deg sweep 

angles

• Input and output channels.

Case Study

70% radius

ɸ Pitch axis
10

Case Studies

baseline 5 deg 10 deg

15 deg 20 deg
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• Time series 0 deg and 20 deg at 14 m/s wind

Case Study
12

Case Study

14 m/s 

0 deg sweep

14 m/s 

20 deg sweep

- 5.6 times slowed down
13

• The mean power has not shown more than 5% 

variation across the various configurations

Note: This finding needs to be revised as the aero 

marker may need to be adjusted for simple blade 

element momentum and crossflow effects 

o Furling limits power anyways - more investigation needed

o Stall-regulated turbine: possible power increase

• Furling standard deviation slightly reduces with sweep.

Case Study Results
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• Blade tip twist 

• 20 deg sweep doubles the twist at the blade tip

Case Study- ULS from DLC 1.1

0

1

2

3

4

5

6

7

8

Load Cases

Blade Tip Twist Magnitudes [deg]

DLC20degDLC15deg

DLC10deg

DLC05deg

DLC00deg

TipRDzc1

TipRDzc2

TipRDzc3
15

0

0.05

0.1

0.15

0.2

0.25

Load Cases

Minimum Tower Clearance [m]

DLC20deg

DLC15deg

DLC10deg

DLC05deg

DLC00deg

TipClrnc1

TipClrnc2

TipClrnc3

• Blade root bending moment

• 20 deg sweep mitigates UL load by 

some 15%

• 10 deg sweep increases UL load by 

some 15%.

Case Study- ULS from DLC 1.1

0

1

2

3

4

5

6

7

Load Cases

Blade Moment Magnitudes [kNm]

DLC20degDLC15deg

DLC10deg

DLC05deg

DLC00deg

RootM1

RootM2

RootM3

Tower clearance almost unaffected
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• Tower base bending moments

• Twenty degree sweep mitigates UL load by some 15%

• Five degree sweep increases UL load by some 10%.

Case Study - ULS from DLC 1.1

0

50

100

150

200

250

300

350

400

450

500

Load Cases

Tower Moment Magnitudes [kNm]

DLC20degDLC15degDLC10degDLC05degDLC00deg

TwrBsM

TwrBsMzt
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• Blade root bending moments

• Twenty degree sweep mitigates damage equivalent loads 

(DELs) by some 15% (flap) to 20% (edge)

• Ten degreee sweep increases DELs by some 5% (edge).

Case Study - FLS from DLC 1.1

0

0.2

0.4

0.6

0.8

1

1.2

05 deg 10 deg 15 deg 20 deg

DEL /DEL@0deg

Root bending DEL ratios with respect to 

the baseline (m=10)

RootMxb1

RootMxb2

RootMxb3

RootMyb1

RootMyb2

RootMyb3
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• Yaw-bearing bending moments DELs reduced (shaft life)

• Tower-base moments DELs reduced by some 20%

• Twenty degree sweep mitigates DELs by some 20%.

Case Study - FLS from DLC 1.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

05 deg 10 deg 15 deg 20 deg

DEL/DEL@0deg

Yaw-bearing DEL ratios with respect 

to the baseline

YawBrMxp m=3

YawBrMxp m=4

YawBrMxp m=5

YawBrMyp m=3

YawBrMyp m=4

YawBrMyp m=5

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

05 deg 10 deg 15 deg 20 deg

DEL/DEL@0deg

Tower-base DEL ratios with respect 

to the baseline

TwrBsMxt m=3

TwrBsMxt m=4

TwrBsMxt m=5

TwrBsMyt m=3

TwrBsMyt m=4

TwrBsMyt m=5
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Conclusions

• A new ADAMS preprocessor is now available for FAST 7.02 which 

allows for higher fidelity representation of pre-sweep and bend of 

blades.

• A case study on a small wind turbine revealed the capabilities of 

simulating the effect of blade sweep using FAST2ADAMS

• Results show promising effects in terms of load mitigation: 

• ULS decrease by 15% at 20 deg sweep (likely 10%–15%)

• DELs decrease by 20% at 20 deg sweep (likely 15%–20%)

• Little effect on power production (same rotor area) to be 

revised with new aeromarkers, possibly eliminating furling.

• Use sweep to grow the rotors or thin the blades and reduce costs,

but use caution in selecting amount of sweep, as some angles may 

create nonlinear effects on the dynamics of the machine and 

increase loads.
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

For More Information

Rick.Damiani@nrel.gov